Performance of mycology and histopathology tests for the diagnosis of toenail onychomycosis due to filamentous fungi: Dermatophyte and non-dermatophyte moulds.

Improvement of laboratory diagnosis of onychomychosis is important so that adequate treatment can be safely implemented. To evaluate and compare the performance of mycological and histopathological examinations in onychomycoses caused by dermatophyte and non-dermatophyte moulds. Patients with lateral/distal subungual onychomycosis in at least one hallux were enrolled in the protocol and assessed via mycological and histopathological tests. The isolation of filamentous fungi was considered the gold standard. Test performance was evaluated through sensitivity, specificity and positive and negative predictive values. A total of 212 patients were enrolled in the study. Direct microscopy (DM) was positive in 57.5% patients, and cultures in 34.4%. Among these patients, 23.3% were positive for dermatophytes, with Trichophyton rubrum the most frequently isolated, and 86.3% were positive for non-dermatophytes, with Neoscytalidium dimidiatum predominance. Histopathology was positive in 41.0% samples. Direct microscopy showed better sensitivity for non-dermatophyte moulds (P=.000) and nail clipping was more specific for dermatophyte (P=.018). Histopathology of the distal nail plate is a valuable complementary tool for the diagnosis of onychomycosis caused by dermatophytes and direct microscopy is especially useful for non-dermatophyte molds.

Cutaneous murine model of infection caused by Neoscytalidium dimidiatum: a preliminary study of an emerging human pathogen.

Neoscytalidium dimidiatum is an emerging fungus that causes a skin infection similar to dermatophytosis; it affects both immunocompetent and immunosuppressed individuals, and it may invade deeper tissues and organs and cause systemic disease. Little is known about the etiopathogenesis of the infection caused by this fungus, and no standard effective treatment is available. The aim of the present experimental study was to develop an animal model of skin infection with N. dimidiatum. BALB/c mice were inoculated with two fungal strains, and different routes of infection were tested. When challenged intradermally, N. dimidiatum strain HUPE164165 caused skin infection in 67% of the animals whereas strain HUPE115669 did it in 49%. Neoscytalidium dimidiatum was isolated from the skin of 25% of the animals inoculated via epidermal scarification and from 100% of the animals challenged via subcutaneous injection. Mice inoculated intradermally were followed-up during four weeks, and clinical samples were collected on days 3, 8, 15, and 29 after inoculation, corresponding to different stages of infection. The cutaneous infection rate, as measured by the recovery of N. dimidiatum strain HUPE164165 from skin biopsies of animals inoculated intradermally, revealed the presence of infection in 90% of the animals sacrificed at 3 days post-inoculation, 71% at 8, 85% at 15, and 33% at 29. Conidia and hyphae were observed in PAS-stained sections as well as a mild to moderate inflammatory infiltrate in haematoxylin-eosin, although it did not differ from animals inoculated either with T. quinckeanum or PBS. The intradermal route of inoculation was considered to be suitable for the study of skin infection with N. dimidiatum The animal model developed in this preliminary study is the first to allow the study of cutaneous infection with N. dimidiatum and may contribute to further investigations of the aetiology, immunology, pathogenesis and treatment targeting this emerging mycosis.